The invention relates generally to offshore oil and gas development, and more particularly to methods for installing an offshore tower in a deepwater location to facilitate such development.
Conventionally, such towers are called "jackets" and are fastened to submerged surface by means such as piling. Decks and other equipment are installed on the upper ends of such jackets. Such installations, when completed, provide platform means to support drilling, production, storage, and/or processing facilities.
In recent years, considerable research has been directed to the development of procedures and equipment for exploiting oil and gas deposits underlying large bodies of water. In the initial stages of offshore development, exploration and drilling and recovery operations were conducted in offshore waters in locations of relatively shallow water depths, such as from a few feet to 100 or more feet. Recently, however, considerable effort has been directed to exploration and site development in water depths ranging from a few hundred feet to 1,000 feet, or more. Examples of such deepwater oil fields may be found along the Pacific Coast continental shelf and the North Sea.
In order to exploit oil fields existing beneath such substantial depths of water, it is common practice to permanently install a jacket on a submerged surface, using fastening means such as piling. This jacket may be provided with a suitable top structure, or deck, as a base for supporting drilling, production, processing, and/or storage equipment. Such completed installations are often called platforms.
In order to exploit deepwater oil fields, it is necessary that jackets be of greater height than those used in shallow water oil fields. Furthermore, jackets for deepwater, open sea environments must also accommodate substantially greater stress than that generally encountered in shallow water operations. Consequently, suitable jackets for deep water installations are relatively large in both size and weight, and require correspondingly more effort in relation to both transportation to the deepwater site and erection of the jackets at the site.
Prior suggested approaches to the handling and erecting of large jackets offshore have involved techniques described in United States patents such as:
______________________________________ Patent Technique Disclosed ______________________________________ Hekkanen - 3,641,774 (1972) Jacket segments assembled while floating Guy et al - 3,859,806 (1975) Jacket segments assembled while floating Hauber et al - 3,315,473 (1967) Jacket supported on twin barges which are submerged for jacket launching Rosenberg et al - 3,845,634 (1974) Jacket supported on rolling cylinders Pogonowski et al - 3,496,897 (1970) Jacket supported on outrig- ger of one barge and con- nected with pivot and socket of other barge ______________________________________
In addition, a variety of other United States patent disclosures involve single and/or multiple barge launching systems and/or a variety of separable buoyancy systems. Such patents include, by way of example:
______________________________________ Patent Technique Disclosed ______________________________________ Kirby - 2,422,168 (1974) Side launching slides on barge Guenzel - 2,581,098 (1952) Foldable platform with auxiliary buoyancy means Sims - 3,036,438 (1968) Caisson launched with auxiliary floats Alcorn et al - 3,054,267 (1962) Jacket launched with hinged barge section Swanlund Jr. et al - 3,186,180 (1965) Jacket launched from long- itudinal ramp on barge Steitle - 3,347,052 - (1969) Separable, auxiliary buoyancy means Lawrence - 3,633,369 (1972) Auxiliary buoyancy means stripped away from upright jacket Koehler - 3,693,361 (1972) Auxiliary buoyancy units Pogonowski et al - 3,708,985 (1973) Platform monopod with articulated buoyancy units Koehler - 3,815,371 (1974) Auxiliary buoyancy Crout et al - 3,823,564 (1974) Detachable buoyancy raft Koehler et al - 3,859,804 (1975) Detachable buoyancy raft with auxiliary buoyancy means Koehler et al - 3,937,027 (1976) Side launching pivot on barge for jacket ______________________________________
Prior proposals such as those noted above either do not lend themselves to the handling of large jackets with both economy and reliability and efficiency, or require special, often large, flotation equipment, or entail quite complex jacket installation operations.